Environmental cocaine concentration effects on Danio rerio development

The illicit drugs can be considered the latest group of emerging pollutants, widespread in the aquatic environment, as a consequence of the enormous increase in the global consumption of these drugs. Although their strong pharmacological activities let foresee toxic effects to the aquatic organisms, only few studies have been performed to evaluate the real risks to the aquatic species. In particular, previous data showed that when the European eels (Anguilla anguilla) are chronically exposed to environmental cocaine concentrations, they bioaccumulate cocaine in their tissues, especially muscles and undergo endocrine and histological alterations. Therefore, the aim of the present study was to evaluate if environmental cocaine concentrations could affect the development of the zebrafish, Danio rerio, a well-known bioindicator of environmental pollution. Toxicity tests at environmental cocaine concentration (20 ng/l) were performed on zebrafish embryos and larvae. No mortality and phenotypic alterations were revealed on both developmental stages at 24, 48 and 72 h of cocaine exposure. However sections of larvae fixed in Bouin’s solution, embedded in paraffin for light microscopy and stained with ematoxylin and eosin (HE) showed alterations of the muscle tissue, that appeared reduced in thickness and disorganized. An increase of apoptosis was also observed in the tail cells of larvae by acridine orange stain in whole mount. These results agree with unpublished data, showing similar changes in the muscles of A. anguilla, chronically exposed to cocaine. Therefore, the present results indicate that cocaine, at environmental concentrations, could impair the skeletal muscle development in zebrafish larvae.